This report describes the effect of welding conditions on porosities for electron beam welding of 50 Kgf/mm2 class nodular cast iron (6, 12, 18 mm thickness) with SUS304 (0.5 mm thickness) as insert metal. The results obtained in this experimental investigation are summarized as follows; (1) Amount of porosities of the fusion zone remarkably decreases by pretreatment annealing (950°C ×5 hr). (2) For the range of ab value from 0.7 to 0.9, well type beads are formed and no crack is observed. (3) For the range of ab value more than unity, wedge type beads are formed and weld cracks occurred and porosities increased. (4) Amount of porosities has tendency to decrease as beam current increase and to increase as welding speed increase. (5) For base metal of 6, 12 mm thickness, amount of porosities is remarkably decreased by 1 pass weld and for 18 mm thickness remarkably decreased by 2 passes weld. (6) Under optimum welding conditions, sufficient strength of the welded joint can be obtained.
Pipeline installation requires the use of a welding method presenting high pipe-laying efficiency and therefore high welding speed. The present report describes the development of welding procedure by the automatic one side downhill welding method using high-current-density GMAW with regard to the girth welding of pipe. In this method, the groove root is made tight and non-gapped, and welding is performed in the narrow gap with little deposit metal, in order to shorten the pipe alignment and welding time. An appropriate procedure for this method was established by developing the downhill welding which uses copper backing on the pipe inside and small diameter solid wire on the pipe outside. When the standard welding conditions are deviated from, the welding arc will touch the copper backing sometimes causing the copper to deposit on the root bead. This deposition of copper on root beads causes not only cracking of beads, but decreasing pipelaying efficiency due to consumption of copper backing. As a result of various researches, this problem was resolved by preparing another groove on the pipe inside in addition to the groove on the pipe outside. The use of the improved shape of groove expanded the zone of appropriate welding conditions for root pass toward the high-speed welding side. The built-up sequence was divided basically into three kinds of passes, the root pass, intermediate pass and cap pass, and each pass was expressed graphically to facilitate the selection of welding conditions for assuring no welding defects and high welding efficiency. This welding method was applied into a welding system with the development in computor control technique and with the development in internal clamp.
Fatigue crack propagation path in wled metal or H.A.Z. is not always straight and also not vertical to the stress axis. In this report, the affection of the hard region to the fatigue crack propagation direction was investigated. The hard region was found to influence the fatigue crack propagation direction. As the plastic zone shape became asymmetric to the vertical direction to the stress axis, fatigue crack was beginning to get inclined. The fatigue crack propagation direction was related to the difference of the crack opening displacement of each side. By the fractography, symmetric striation was observed where the crack propagated straitly, and also asymmetric striation and secondary crack which grew out of slip band crack were observed where the crack inclined.
The digging action of arcs and behavior of molten pool during submerged arc welding have been analized by X-ray fluoroscopic observation. Under the condition of normal bead, molten pool is stable and some molten layer of metal is formed beneath the electrode. On the other hand, under the condition of undercut or humping bead, exposed solid surface is observed beneath the electrode. In two electrode tandem welding with respect to high speed welding, there is a optimum ratio of the trailing electrode current (IT) to the leading electrode current (IL). This is owed to that the effective arc pressure of IL acting to the gravity head of molten metal is decreased by increase of the arc pressure of IT. When IT/IL is smaller than the optimum ratio, the effective arc pressure acting to the gravity head of molten metal is given by IL. But when IT/IL is larger, the effective arc pressure is changed to be given only by IT. Undercut bead is formed when these effective arc pressure become larger than total gravity head of molten metal. The effective arc pressure of each electrode become equivalent and lowest at the optimum ratio of IT/IL ≈ 0.7.
For purpose to obtain she fundamental data of securing the reliability of welded joints, the establishment of welding control technique to make weld defects of arc welded joints in the natural condition, the design and trial making of ultrasonic point focussed probe in order to detect quantitatively planar defects and their application were carried out. And also, effects of the lack of penetration with one side welding of SM50B steels on the fatigue test results of welded joints were investigated. The main results are as follows; (1) Relation between the lack of penetration and welding condition in gas metal arc (GMA) welding were made clear. (2) The point focusing angle probe using spherical tansduser in ultrasonic detecting method was pplied to the measurement of the size of lack of penetration. In case that the root face of butt welded joint was gas cut, the detecting accuracy was about±0.5 mm. However, in case that there were blow-holes or some weld defects on the way of passing of ultrasonic beam or near the root, the size of planar defect was often mistaken. And also, in case that the root face was closely attached by welding, the detection of lack of penetration was often difficult. (3) The uniaxial stress fatigue strength of arc welded joints for SM50B steels which have the lack of penetration of about 2-4 mm in depth, without reinforcement and finished surface, was extremely lower than that of base metal and welded joints which have full penetration, without reinforcement and finished surface. And the fatigue strength of arc welded joints with reinforcement showed the intermediate values between that of base metal or welded joints which have without reinforcement and finished surface and that of welded joint which have the lack of penetration of about 2-4 mm in depth, lowered fairly in comparison with that of base metal. These test results were discussed with non-linear fracture mechanics, consequently, the fatigue limits of welded joints are evaluated with effective notch depth as a whole.
The effects of the welding methods, heat input and heat cycle on the mechanical properties at elevated temperature for the 308 type stainless steel weld metals rae investigated and the following results are obtained. 1) Creep rupture strength for the TIG arc weld metals is large about 2 kg/mm2 compared with that for the submerged arc weld metals, and creep rupture elongation for the submerged arc weld metals is large compared with that for the TIG arc weld metals. 2) The oxygen contents of the submerged arc weld metals are more than ten times as much as those for the TIG arc weld metals. The oxygen in the weld metals forms the inclusion. 3) The inclusions in the submerged arc weld metals are from about 0.2 to 0.4 μ in diameter, and are distributed at a mean interval of about 4μ in length. These inclusions decrease the both strengthes and increase the creep rupture elongation. 4) The hardness and the tensile rupture elongation for the lower heat input submerged arc weld metal are high compared with those for the higher heat input submerged arc weld metal. 5) Structures of solidification, dendrite, δ ferrite network for the low heat input submerged arc weld metal are fine compared with those for the high heat input submerged arc weld metal. It is supposed that these fine structures increase the hardness and rupture elongations at tensile test. 6) As the followed thermal cycles increase the room temperature hardness for preceded weld metals, these thermal cycles have no effects on the tensile strength at elevated temperature and creep rupture strength of the preceded weld metals. These results are caused by the disappearance of the difference in the structures between the followed and the preceded weld metals during tests at the elevated temperature.
The stress concentration factor and the stress intensity factor at the place, where fatigue and cold cracking frequently occur during manufacture and in service, have been studied using numerical analysis. This paper is the first part of three-part paper on the above subject. It firstly deals with the characteristics of the histgram, average value, and deviation of factors involved in the reinforcement of welded joint produced by various welding processes such as SMAW, SAW, EBW, CO2W. The equation is second-ly derived that related the stress concentration factor with the factors involved in the reinforcement of weld. The results are summarized as following: (1) The root radius of shielded manual arc welded joint was large in comparison with that of other welding processes such as EBW, CO2W, SAW. (2) There did not exist the significance concerning the correlation among the factors involved in electron beam welded joint. (3) The difference between the real value and the predicted value of the stress concentration factor was less than or nearly equal to 0.3.
Influences of chromium and molybdenum on the reheat cracking sensitivity of the high strength steels and Cr-Mo heat resisting steels were investigated using 20 synthetic Cr-Mo steels melted in our laboratory. These steels contained 0 to 5 wt%Cr and 0.25 to 1.5 wt%Mo. Cracking sensitivity were evaluated in terms of the criticl restraint stress obtained by the modified implant method for the reheat cracking. The results are summarized as follows. 1) When the chromium content was smaller than about 1 wt%, the cracking sensitivity increased with the increase of chromium content, but when it exceeded about 1 wt%, the cracking sensitivity decreased conversely. 2) The harmful effect of molybdenum was maximum when the chromium content was about 1 wt%. 3) The combined influence of chromium and molybdenum was shown by means of the contour lines of the critical restraint stress in the Cr-Mo contents diagram.